Numerous articles of footwear and methods for manufacturing the same are known in the prior art. The simplest of these constructions includes stitching together overlapping layers of leather or cloth to form an upper covering for the foot and then using an adhesive to attach a preformed outsole. The adhesive may be applied with a brush, or alternatively, as in U.S. Pat. No. 3,988,797 to Tornero, a shoe upper may be integrally joined to a preformed rubber outsole by placing both the shoe upper and outsole in a mold cavity and then injection molding an outsole adherent therein in order to join the outsole to the upper. Other constructions include forming an injection molded outsole and/or midsole and integrally joining the upper during the molding process of the sole unit. For example, U.S. Pat. No. 4,245,406 to Landay et al. discloses an athletic shoe in which an upper and a preformed rubber outsole are joined by a foamed polyurethane, injection-molded midsole. The shoe is manufactured by treating the inner surface of a preformed rubber outsole to prepare it for bonding to polyurethane, inserting the treated sole into the bottom of a mold, mounting a preformed upper on a last, lowering the last and closing the mold, with the last spaced above the rubber outsole, injecting a charge of foamable polyurethane between the outsole and the last, and allowing the polyurethane to foam under self-generated pressure to form the midsole and to bond with the outsole and upper.
Each of the above constructions utilizes an injection molding process to form all or part of the sole unit or to adhere the sole to the preformed upper. Further methods of construction, such as those disclosed in U.S. Pat. No. 4,150,455 to Fukuoka and U.S. Pat. No. 4,266,314 to Londner epouse Ours, extend the injection molding to improve the upper portion of the article of footwear. Fukuoka disposes an upper base in a mold and then injects a synthetic resin material for the upper into the upper molding cavity. After the upper portion of synthetic resin is cooled, the upper is transferred to the mold for the sole and the sole portion of synthetic resin is injected into the sole molding chamber. After the sole portion of synthetic resin is cooled, the finished molded shoe of synthetic resin is removed from the mold. Londner epouse Ours discloses a lining of leather or other suitable material for the shoe upper onto which are overmolded two overlapping portions of plastic materials of different types. The first layer of plastic material injection molded in direct contact with the lining and covers the entire upper while the second injection molded portion constitutes a stiffening reinforcement that surrounds only the rear counter of the upper and a thin intermediate sole. An outer wearing sole is then added to the article of footwear. The injection molding processes utilized in the above prior art, whether to mold only the sole or portions of the upper as well, have the disadvantages of requiring an additional finishing step for the upper of the article of footwear, injecting parts having difficult areas to fill while being limited to only one foam material per pour; these requirements limited the available foams to those which provided acceptable cosmetics, bonding strength and split tear resistance, no air bubbles, exposure to the elements survival, whiteness/color retention, and were generally flash control foams, such as DALTOPED and similar polyester and polyether based elastomer systems offered by ICI Americas Inc.